Page Contents
Quick Answer
Insulating an AC line set is not strictly required by code, but it is highly recommended for several reasons:
- Insulation helps prevent condensation from forming on the cold lines, which can lead to water damage.
- It protects the lines from physical damage.
- It improves system efficiency by reducing heat gain/loss in the lines.
- It prevents energy loss and higher operating costs.
While some HVAC contractors may say it is not necessary, most experts agree that insulating line sets is a good practice that provides meaningful benefits. The small upfront cost is worth it long-term.
What is an AC Line Set?
An AC line set refers to the pair of pipes that connect the outdoor condenser unit to the indoor evaporator coil in a split air conditioning system. One line carries the liquid refrigerant while the other returns the gaseous refrigerant back to the compressor.
Line sets are usually made of copper tubing with flare fittings at the ends to connect the components. They are installed between 3 to 50 feet in length, depending on the physical layout of the house or building. Insulated line sets have a foam sleeve fitting snugly around the copper lines.
Some key facts about AC line sets:
- Sizes range from 1/4” to 1” in diameter for residential systems.
- Larger commercial/industrial lines can be 1 1/8” to 2 1/8” in diameter.
- Tubing wall thickness ranges from 0.020” to 0.049”.
- Common insulation materials are polyethylene foam, rubber foam, or fiberglass.
Properly installed and insulated line sets are critical for achieving optimal performance in a split air conditioning system.
Should Line Sets be Insulated?
Insulating an AC line set is not an absolute requirement as per international mechanical codes. However, most HVAC experts strongly recommend insulating the line set whenever a new system is installed or an old line set is replaced.
Here are some of the main benefits of insulating AC line sets:
Prevents Condensation
The cold liquid line can “sweat” and accumulate major condensation without insulation in hot, humid climates. The water can drip and cause mold, mildew, and structural damage. Insulation prevents this sweating and protects ceilings, walls, and floors.
Protects from Damage
Insulation provides a protective barrier that protects copper lines from dings, scratches, and punctures during maintenance or when objects fall against it. This prevents costly refrigerant leaks.
Maximizes Efficiency
Insulation minimizes heat transfer in the cold vapor line and hot liquid line. This preserves the cooling capacity and SEER rating, while reducing utility costs. Uninsulated lines contribute to higher energy consumption.
Maintains Refrigerant Temperature
Keeping the refrigerant cold in the line set prevents premature boiling or flash gas formation before it reaches the indoor coil. This improves heat transfer, cooling, and dehumidification.
Reduces Noise
Insulation dampens vibrations and noise as refrigerant flows through the line set. This minimizes annoying rattles and vibration transmission.
Avoids Sweating and Corrosion
Insulation protects the copper tubing from acidic condensate runoff that can lead to corrosion and pinhole leaks over time.
Provides UV Protection
Insulation shields copper lines from ultraviolet rays that can accelerate degradation of the tubing material when exposed to sunlight.
Recommended Insulation Thickness
The amount of insulation thickness needed depends on the line set diameter and operating refrigerant temperatures. The colder the system runs, the thicker the insulation should be to prevent condensation.
Here are some general guidelines on insulation wall thickness from ACCA Manual D:
| Line Set Diameter | Minimum Insulation Thickness |
| 1/4″ | 3/8″ |
| 3/8″ | 3/8″ |
| 1/2″ | 1/2″ |
| 5/8″ | 1/2″ |
| 3/4″ | 1/2″ |
| 7/8″ | 1/2″ |
| 1 1/8″ | 1″ |
For chilled water or refrigerant suction lines below 50°F, increasing the insulation thickness to 1″ is recommended to prevent moisture issues.
The key is ensuring a tight seal between the copper line and insulation without any air gaps. The insulation should be snug to maintain maximum efficiency.
How to Insulate an AC Line Set
Insulating an AC line set is easiest before it is installed and purged with refrigerant. But it can also be done on existing lines using slit foam tubing. Here are the basic steps:
Cut Insulation to Length
Cut sections of foam pipe insulation to match the line set lengths. Seal the ends of each section. Leave excess length to cover fittings.
Slit Sections Lengthwise
Use a sharp utility knife to slit one side of the insulation tube lengthwise so it can open up. Try not to cut all the way through.
Spread Open the Insulation
Gently spread open the slit insulation so that it wraps around the line when fitted over it.
Fit Insulation Over Lines
Gently fit the slit section of insulation over the line, sandwiching the line inside. Take care not to scratch or dent the line.
Seal Seams
Use insulation tape, adhesive or mastic to seal the seam of the slit insulation and create an airtight barrier.
Cover Fittings
Build up insulation around fittings and joints to eliminate any gaps in coverage. Seal ends.
Support Insulated Lines
Use metal hangers or straps designed for insulated lines to properly support their weight.
Common Mistakes to Avoid
Here are some common mistakes that should be avoided when insulating AC line sets:
- Failing to insulate the suction/vapor line along with the liquid line.
- Not covering fittings, joints, and valves.
- Leaving gaps between insulation segments or at seams.
- Using insulation with rips, tears, or holes.
- Allowing the line set to touch other hot equipment or ductwork.
- Letting condensation drip onto the air handler or other electronics.
- Not providing proper support for insulated lines.
- Sizing insulation too small for the line set diameter.
Properly insulating the line set without any flaws is critical to realizing the full benefits.
Split Line Set Insulation
For existing line sets, it can be difficult to insulate the whole length at once. In this case, slit insulation can be installed in sections:
Outdoor Unit Lines
Insulate the sections of the line set that are exposed to outdoor ambient temperatures first. Protect from UV and prevent heat gain/loss.
Indoor Sections
Insulate the indoor portions of the line set in conditioned space to maximize efficiency. Prevent condensation near ceilings and walls.
Accessible Areas First
Insulate the accessible sections of line set first, where the insulation can easily be wrapped around the lines.
Hard-to-Reach Areas
Use short insulation segments to build up coverage in tight areas around bends and fittings.
Doing the accessible areas first provides partial benefits while difficult spots can be addressed over time.
Choosing the Right Insulation
Here are some key factors to consider when selecting the best insulation for AC line sets:
Insulation Material
Closed-cell elastomeric foam provides the best air sealing properties. Polyethylene foam insulation is also suitable. Fiberglass should be avoided due to moisture absorption issues.
Density/Weight
Higher density insulation between 3-6 pounds per cubic foot provides better efficiency and moisture resistance compared to lower density insulation.
Temperature Rating
Look for insulation rated for use on lines from -40°F to 200°F to withstand the temperature extremes.
Moisture Resistance
Choose insulation with vapor barrier properties to prevent condensation issues. Closed-cell foams work well.
Tube or Slit-Tube Type
Slit tube insulation with adhesive sealing strips allow for easy retrofit on existing line sets.
Proper Thickness
Match insulation wall thickness to the line set diameter following guidelines from ACCA Manual D.
Indoor/Outdoor Use
Select insulation approved for exterior UV and weather exposure when insulating outdoor sections.
Proper insulation helps ensure an energy efficient AC system with lower operating costs and a longer service life.
Key Takeaways
- Insulating AC line sets is highly recommended, though not an absolute requirement.
- Benefits include preventing condensation, protecting lines, improving efficiency, reducing noise and avoiding corrosion.
- Recommended insulation thickness varies based on line diameter and refrigerant temperatures.
- Slit foam tubing can be installed on existing line sets segment-by-segment.
- Avoid common mistakes like incomplete coverage, gaps at seams, and undersized insulation.
- Match insulation properties to application needs including temperature rating and moisture resistance.
Conclusion
While the building codes leave insulation on AC line sets open as an option, most HVAC experts view it as a required best practice. The benefits clearly justify the minimal upfront cost. It represents a cheap way to maximize system performance and avoid problems. With the availability of split tube insulation, there is no excuse not to insulate AC line sets during new installations or retrofits. Just be sure to avoid any gaps and completely seal the insulation for best results. Following proper line set insulation practices will pay off every cooling season.